Boise State UniversityScholarWorks
2019 Graduate Student Showcase Graduate Student Showcases
4-12-2019
Application of Infrared Thermography in PavementInspectionAidin J. GolrokhBoise State University
Aminul Islam
Yang LuBoise State University
Aidin J. Golrokh, Aminul Islam, Dr. Yang Lu*
Department of Civil Engineering
Contact information: [email protected]. OF CIVIL ENGINEERING
• Infrared Thermography (IRT) is an effective non-destructive
testing method in the field of pavement inspection. The method
can be widely used for inspection of pavements and bridge
decks. Deployment of IRT procedure is straight-forward and no
direct contact is required. Its one-side deployment makes it
favorable for bridges in which we have access to only one side
of the structure.
• IRT captures the temperature gradient of concrete pavement
surfaces. When exposed to heat, delaminated parts of concrete
will interrupt the heat transfer which will cause temperature
gradient on top of the surface of the pavement which can be
picked up by thermal camera.
INTRODUCTION METHODOLOGY
RESULTS & DISCUSSIONS
RESULTS & DISCUSSIONS
CONCLUSION
BACKGROUND AND PHYSICS
• The following equations govern the physics of thermography in
our studies.
Heat transfer in porous medium:
𝜌𝐶𝑝 𝑒𝑓𝑓
𝜕𝑇
𝜕𝑡+ 𝛻 ∙ 𝑞 = 𝑄
Where 𝑞 = −𝑘𝑒𝑓𝑓 𝛻𝑇 𝑎𝑛𝑑 keff = (1 − ɛp) kr + ɛp kw
Stefan-Boltzmann law:
W=ɛσT4
Where W is radiant flux, ɛ is emissivity and σ is Stephan-
Boltzmann constant (equal to 5.67 × 10−8𝑤𝑎𝑡𝑡𝑠/𝑚2/𝑘4)
Wien’s displacement law:
λm=𝑏
𝑇
Where λm is the wavelength, T is temperature and b is Wien’s
displacement constant (equal to 2897 µ𝑚/𝐾)
Observation rate for thermography:
𝑡 ≈𝑧2
𝛼and 𝑐 ≈
1
𝑧3
Where z: depth, t: time, α: thermal diffusivity (for concrete is 0.53)
Research study #1: Subsurface defect assessment and IRT
Research study #2: Surface defect assessment & IRT
Research study #3: Effects of weather conditions on IRT
• Subsurface delamination (such as air void) has a different
thermal conductivity compared to bulk concrete and asphalt
hence acts as an heat insulator.
• Depth of delamination has an effect on the temperature
gradient that it generates on the surface of specimen.
Delaminations located deeper from the surface have lesser
effect on the generated temperature gradient.
• In order to mimic air void defects,
styrofoam cubes were inserted in
different depths inside of the concrete
domain.
• Thermal and visual images of the
specimen were recorded by a
thermal camera (FLIR 430sc).
Visual image Thermal image
• A real-time thermal imaging-based system for asphalt pavement
surface distresses inspection and 3D crack profiling is proposed
in this study.
• A mobile setup is introduced which is capable of collecting a
series of both thermal and visual images from the pavement
surface.
• A computer program is developed for segmenting the thermal
images.
METHODOLOGY
Field test set-up
Image processing
• A full-scale experimental study of the effects of different climatic
conditions on infrared thermography and surface delamination
assessment in concrete structures is presented in this study.
• For laboratory experiment, a controlled laboratory testing system
is developed which is capable of imitating a variety of weather
conditions that can affect thermography.
Thermal and visual images
• Digital image base 3D surface scanning technology is used to
simulate the crack.
• The multi-physics experiment is simulated using finite element
software.
3D scanning of the crack
Results from research study #1
Results from research study #2
• A temperature profile along marked line on the sample (shown in
thermal image) is plotted in the following graph. Simulation
results along the same line in computer model is also shown.
• Simulation results had similar trend as the experimental results
• In this study a relation between crack temperature and its profile
is studied.
• Correlation between temperature and depth of crack was higher
(R2=70%) compared to the temperature and width of crack
(R2=50%.). The temperature data represented in the graphs are
normalized based on the localized average surface temperatures.
• The segmented image shows the area on top of the sample
affected by the presence of the delamination.
Results from research study #3
• Temperature reading during the
cooling cycle shows the effect
of humidity (= 80%) and wind
(=3.5 m/s or 7.8 mph) on the
temperature reading of the
camera.
• Heating under normal
conditions (humidity = 16% and
no wind) is taken as control.
• Temperature readings for cracks with different depth sizes based
on the results from experimental data and the computer model
are show in following graphs
• Temperature change during the cooling cycle follows the same
trend in both the experiment and the simulation.
• Thermography can be used for the inspection of subsurface
delamination inside concrete and asphalt pavements. Studying
the effect of delamination depth on the temperature gradient will
assist the better understanding of the effectiveness of
thermography in application.
• A new approach based on normalization of the temperatures
shows that deeper cracks have higher temperature in the
temperature profile that is captured by using thermal camera.
• It is also found that cracks heat up more and lose heat slower in
humid condition. Also, deep cracks are more prone to the effects
of humidity than shallow cracks.
• Studying different aspects of IRT may help in development of a
system to automatize the inspection of surface and subsurface
defects in pavements by using thermal imagery.
(1-ε)*τ*Wrefl
Atmosphere
(1 – ε)*Wref
Target
ε*Wobj
ε*τ*WobjHeat Source
(1-τ)*Watm
Thermal Camera
TObject = 4 𝑊𝑇𝑜𝑡𝑎𝑙− 1−ɛ .𝜎.𝜏. 𝑇𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑
4−𝜎. 1−𝜏 .(𝑇𝐴𝑡𝑚𝑜𝑠𝑝ℎ𝑒𝑟𝑒)
4
ɛ.𝜎.𝜏
• Each pixel of infrared thermal image is representing the
temperature identity of that specific location on the surface of the
specimen. However, this temperature value is not a direct result
of converting emitted energy to temperature reading. The major
emission entities that are received by the thermal camera are
Target emissions (EObject), Surrounding emissions reflected from
the surface of the object (EReflected) and atmosphere emissions
(EAtmosphere).
Defect
Concrete specimen
Detected surface by IRTHeated surface